(v13) Color component order and color models

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

The device-dependent color models, for both input color space and output color spaces, are referred to as DeviceGray, DeviceCMYK, and DeviceRGB, but for output these names each cover a family of raster formats, because there may be single-bit or multi-bit pixels, different ordering of the color components, and different interleaving.

It is important to be clear about the difference between the input color space (that is, how the numbers in the PostScript-language jobs are to be interpreted) and the output color space (that is, the meaning of the numbers in the rasters produced). The relationship between the input and output color spaces is expressed by Figures 4.5 and 4.6 in [RB2]. This chapter is concerned with setting up the output color space.

For color rasters, the order of the color components can be varied. A 32-bit pixel interleaved raster using the subtractive primaries (DeviceCMYK ) could have the color components of the pixels in the order Cyan – Magenta – Yellow – Black, or Black – Yellow – Magenta – Cyan, or any other combination.

This also applies to band-interleaved formats, and also to Red – Green – Blue rasters (though it would be quite rare for these to be reordered).

Overprinting is applied to DeviceCMYK multi-bit rasters—individual components are knocked out or overprinted according to the setoverprint operator, as for separations (see (v13) Knockouts and overprinting). However, overprinting is ignored for DeviceRGB multi-bit rasters.

The Harlequin RIP does not support DeviceCMY or DeviceRGBK output color models directly. These models are referred to in recent Adobe documents (for example [EXTN2014]). However 24-bit CMY can be produced by using RGB space and inverting it using the NegativeJob user parameter or NegativePrint page device key, and similarly RGBK can be produced by inverting CMYK.